It is also well known, notably through document FR-2,884,555, to use the calorific energy conveyed by the exhaust gas of internal-combustion engines, in particular those used for motor vehicles, as the hot source providing heating and vaporization of the fluid flowing through the evaporator.
This allows to improve the energy efficiency of this engine by recovering a large part of the energy lost at the exhaust in order to convert it to an energy that can be used for the motor vehicle through the Rankine cycle loop.
As it is widely known, using an aqueous working fluid in a Rankine cycle loop affords the advantage of having characteristics that allow to obtain a maximum saturation curve while having the advantage of not being dangerous.
However, this water has the specific feature of having a freezing point at low temperatures (around 0° C.) and antifreeze additives such as glycol are usually added thereto in order to lower this freezing point to acceptable temperature levels, of the order of −15° C. to −30° C.
Adding such additives has the drawback of changing the characteristics of the water, in particular its vaporization characteristics, and the hot source from the exhaust gas may be insufficient to perform this vaporization in a satisfactory manner.
Furthermore, in the course of time, this additive-containing water undergoes unpredictable aging as the liquid/vapour phase changes take place. This unpredictable aging can lead to incomplete phase changes for this water, which generates Rankine cycle loop dysfunction.
In other Rankine cycle closed loop types, this additive-containing water is replaced by pure water with very good energy recovery properties.
However, using such pure water does not prevent freezing in any way when the ambient air is at very low temperatures.
Freezing can cause irreversible damage to the loop constituents, such as exchanger cracking, pump destruction or even bursting of the pipes connecting the constituents.
As better described in French patent application No. 2,956,153, the applicant has overcome these drawbacks by providing a device and a method that prevent this water from freezing.
The working fluid is therefore drained off the closed loop and collected in a storage tank when this loop is at standstill.
The applicant has improved this device even further so as to facilitate emptying of the closed loop in a simple and economical manner to prevent the water from freezing, without using the circulation pump. Indeed, the circulation pump of the closed loop does not functionally allow complete emptying and filling of this loop, its technology often requiring unidirectional operation under load.